Thermographic copy machine comprising means to tension the sheet composite in the irradiation zone



April 14, 1964 E. WEDEL 3, ,3 THERMOGRAPHIC COPY MACHINE COMPRISING MEANS T0 TENSION THE SHEET COMP OSITE IN THE IRRADIATION ZONE Filed May 4, 1960 22 flvvavrae 5 2; [kW/xv M-WEL United States Patent 3,129,325 THERWOGRAPIIIC C(BIY MACHINE COMPRISING MEANS T0 TENSION THE SHEET COMPOSITE IN THE IRRADIATION ZGNE Erwin Wedel, St. Paul, Minn assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed May 4, 196%, Ser. No. 26,849 Claims. (Cl. 25'065) This invention relates primarily to thermocopying machines as applied to the thermographic reproduction on heat-sensitive copy-sheets of differentially radiation-ab sorptive printed or other graphic originals, and is con cerned particularly with novel and simplified means for maintaining the copy-sheet and original in close heatconductive pressure-contact during irradiation.

The simplicity of machines constructed in accordance with the present invention permits substantial reduction in s ze of the machine, reduces the number and complexity of component parts required, and in general provides a much simplified and, therefore, more economical and more easily constructed and serviced thermoprinting machine than has heretofore been available. The unit is particularly useful in making one or two copies of occasional memos, letters, or other items of business correspondence. Operation is by the thermographic reproduction principle, as described, for example, in Miller Patent No. 2,740,896, and involves the brief intense irradiation of the printed or other differentially radiation-absorptive original while in close pressure-contact with a heat-sensitive copy-sheet.

The invention will now be described in terms of a specific exemplary embodiment and as illustrated in the accompanying drawing in which:

FIGURE 1 is a schematic side elevation, partly in section, showing the positioning of the rollers and lamp element;

FIGURE 2 is a similar side elevation showing an arrangement of drive gears for the operation of the rollers;

FIGURE 3 is a somewhat schematic plan view further showing the arrangement of parts in the copying machine;

FIGURE 4 is a detail view, partly in section, illustrating a method of mounting the lamp;

FIGURE 5 is a view, partly in section, of the print roller; and

FIGURES 6 and 7 are plan-view and side elevation respectively of a carrier screen member useful in the operation of the printer.

As indicated in FIGURE 1, the apparatus consists essentially of a printing roller 10 towards which are urged, by forces represented by arrows F and F first and second drive rollers 11 and 12. A source 13 of radiation faces the printing roller 10 midway between the two drive rollers and is here illustrated as consisting of a truncated elliptical reflector 14 and a tubular incandescent-filament lamp 15, both shown in cross-section. A feed table 16 faces the nip of rolls 10 and 11, and a scraper blade 17 contacts the advancing surface of the roller 10 at a point beyond the second drive roller 12. Switch 18 is centrally mounted at feed table 16 so that the switch is actuated on feeding of copy material into the machine, and switch 19 is located beyond the second drive roller 12, the switch arm passing through a slot in the arcuate guide plate 19a.

FIGURE 2 illustrates typical hearing or interconnections between the several rollers. A main drive gear 20 is carried by the shaft 10s of the roller 10 and intercon. nects with first small idler gear 21 carried on shaft 219 and second small idler gear 22 carried on shaft 22s. These in turn interconnect respectively with first large idler gear 23 on shaft 23s and second large idler gear 24 on shaft 3,129,328 Patented Apr. 14, 1964 24s; and these again interconnect respectively with first drive gear 25 mounted on shaft 11s of the first drive roller 11, and second drive gear 26 mounted on shaft 12s of second drive roller 12.

The gear ratios and roller diameters are so selected as to provide rotation of rollers Ill and 11 at the same surface speed, while the roller 12 is driven in the same direc tion but at a somewhat greater surface speed. It will therefore be seen that a flexible web placed in contact with the surface of the printing roller 11) and beneath both of the drive rollers 11 and 12 will be held under considerable tension while advancing at the surface speed of the printing roller.

The printing roller 10 has a smooth rigid surface, being ordinarily constructed of metal as will be pointed out more in detail hereinafter. On the other hand, the drive rollers 11 and 12 are provided with compressible surfaces, for example consisting of a rubbery sleeve over a steel shaft; and these rollers are urged under considerable force radially towards the center of the printing roller 10. These forces are conveniently applied by means of coil springs, not shown.

The several components are mounted, as shown in FIG- URE 3, on a base 31) and supported on brackets 31, 32. A portion of bracket 32 is indicated also in FIGURE 2 by dotted lines. Shaft Itls passes through each of brackets 31 and 32. Shafts 21s, 22s, 23s and 24s are mounted directly on bracket 32. Shafts 11s and 12s are mounted on movable lugs 33 and 34 respectively, indicated by dotted lines in FIGURE 2, the lugs being pivotally attached to the bracket members around the shafts 23s and 24s in the case of bracket 32, or at equivalent points on bracket 31. V

A motor unit 35 drives the shaft 10s through suitable sprocket wheels 36, 3'7 and interconnecting chain, here indicated by a broken line. Suitable relays are provided in switching unit 33, from which electrical connections are made to the several components as needed and to which connection is made from an external source of power. The entire unit may be enclosed within a suitable protective cover or case if desired, and made easily portable by the addition of suitable fasteners and handles.

The brackets 31, 32, in addition to supporting the several components previously indicated, also support the radiation unit 13, for example by means of mountings as indicated in FIGURE 4 in connection with bracket 32. Two L-shaped members 41, 42 bolted to the bracket 32 provide support for adjustment screws 43, 44 respectively which in turn adjustably support blocks 45, 46 fitted onto the extended framework of the truncated elliptical reflector 14. The lamp 15 of FIGURE 1 is supported at the inner optical axis of the reflector by end-plate means, not shown. The reflector is positioned so that its outer optical axis falls just above the surface of the printing roller. If desired, suitable cam or screw means may be provided in place of the adjustment screws for quickly adjusting the position of the reflector.

The printing roller 10 is shown, partly in section, in FIGURE 5, and comprises two tubular end portions 51 and 52 and three intermediate ferromagnetic ring-like portions 53, 54, and 55, the latter being permanently magnetized in an axial direction and arranged with like poles in opposition. The end portion 51 is circumferentially grooved at 5'6 and the entire roller is held together by opposing end pieces of which piece 57 is here shown in section, snugly frictionally fitting within the tubular end portions 51, 5-2 and around the shaft 10s. The switching lever of switch 19 lies within the groove 56 while the switch is in off position, as illustrated also in FIGURE 1.

The apparatus is employed in conjunction with a carrier screen member 60 illustrated in FIGURES 6 and 7 a v as comprising a flexible base 61' bonded along its forward edge across a cover member 63 having a truncated triangular forward portion ending in a thin, rectangular, and preferably slightly arcuate ferromagnetic portion 62, for example a folded stripof thin steel. In use, the heatsensitive copy-paper 64 and the printed or other graphic original 65 are arranged between the base 61 and the cover 63 in the position indicated in FIGURE 7, and the screen member is slid forward over the feed table 16 and between the printing roller 19 and the first drive roller 11. The action closes the switch 18 and actuates the necessary relays within the switching unit 38, starting the motor 35 and driving the printing roller in the direction indicated, and also actuating the lamp 15. An adjustable time-delay relay permits actuation of the lamp at any desired short time interval after closing of switch 18. The magnetic portion 62 is held against the surface of the roller by the action of the magnetic rings 53 55, and the entire screen member therefore passes beneath both the first and second drive rollers 11 and 12, past the switch 19 which is thereby brought to the on position, and continues until lifted from the magnetized surface by the scraper blade 17. Rotation of the printing roller continues until the screen member has passed the location of the switch 19, which then returns to the oiff position, de-actuating the pertinent relays and shutting off the lamp and motor 35. A guide 19a may be included if desired for directing the rearward portion of the screen past the switch 19.

A preferred form of carrier screen member employs as the flexible base 61 a compressible sheet material such as a heavy paper coated with a layer of sponge rubber, flocked fibers, or polyurethane foam approximately inch thick. With this base, graphic originals which have been wrinkled or cockled are easily pressed into smooth pressure-contact with the heat-sensitive copy-sheet under the tension provided by the differentially driven drive rollers 11 and'1-2. The compressible base also makes less critical the adjustment of the forces F and F on the rollers 11 and 12. However the compressible base is not essential, and fully effective results are attained with non-compressible webs such as paper, plastic film, or smooth fabric-based sheet materials as the sheet 61.

A variety of plastic film materials may be used as the cover member 6 3, including, for example, polyethylene, polypropylene, polyester, and fluorocarbon polymer films. To be effective for this purpose, the film must be sufficiently heat-resistant so that it does not stretch or deform under the temperatures attained during the copying operation. It must be sufficiently transmissive of theradiation employed, and which in most instances will be largely infrared radiation, so that the radiation is permitted to reach the composite of heat-sensitive copy-sheet and graphic original in sufiicient intensity to permit of effective copying, and without causing any excessive heating by absorption directly in the plastic film. The film may be either smooth or embossed on either or both surfaces, a preferred form having a smoothouter surface and a roughened embossed inner surface, the latter contacting the heat-sensitive copy-paper.

As the carrier screen member is advanced into contact with the surface of the printing roller 11), the correspondingly arcuate thin metallic segment 62 is magnetically attracted to and held in close contact with the magnetized central segment of the printing roller 10, and is thus drawn beneath the first drive roller 11 and subsequently beneath the second drive roller 12' The differential speeds of the two driving rollers then produce tension in the cover member 63 of the carrier screen member 61), pressing the composite of copy-sheet and original against the base 61 and against the convexly curved surfaced the printing roller. At the differential employed, the tens-ion is more than sufficient to provide fully effective pressure-contact, and some degree of slippage therefore occurs between the surface of the drive roller 12 and the cover 63.

Slippage occurs at the point indicated, rather than beneath the first driver roller 11, for a number of reasons. For example, the screen member is in contact with the full quadrant of the printing roller between the drive rollers. The materials of construction and the surface finish of the several rollers and of the screen member are selected so as to provide the higher coefiicient of friction at roller .11.

The forces urging the rollers 11 and 12 toward the roller 10 may also be adjusted as necessary in order properly to provide the desired slippage. Increased pressures are desirable when using an incompressible carrier screen, as heretofore noted, but the power requirements are thereby increased, and the increased tension resulting from increased frictional stress requires a carrier screen of high tensile strength; whereas too low a pressure at rollers '11 and 1.2 may permit angling sidewise movement of the carrier screen, or may provide inadequate tension to impart the required pressure-contact.

The hardness or compressibility of the rubbery jackets provided on rollers 11 and 12 may also be varied if desired. Hard-surfaced rollers have more tendency to permit slippage; excessively soft rollers deteriorate rapidly under the stresses encountered.

In a typical apparatus'constructed and operated in accordance with the principles of this invention, the printing roller 10 has a diameter of 2 inches and has a smooth polish metal surface, the central ring portions being composed of magnetic alloy and the end sections of aluminum. The drive rollers 11 and 12 have each a diameter of /1 inch of which the outer 31 inch is a vulcanized rubber composition having a Shore A scale durometer value of 60-70 and ground to a smooth surface. The several rollers are each 10 inches in length, thereby permitting the reproduction of 8 /2-inch width graphic originals, as customarily employed for business correspondence. The lamp 15 likewise is 10 inches in length and requires a power input of about 1,000 watts, operatingat volts A.C. The surface speed of the printing roller .10 is within the range of about -160 inches per minute, but may be more or less depending on the intensity of the irradiation, the type of copy-paper to be used, and perhaps on other factors. The ratio of the surface speed of roller 12 to the surface speed of rollers 1t and 11 is 6/5, although ratios greater or smaller than this value may also be employed. The force F applied at each end of roller 11 is about 7 pounds; the force F applied at each end of roller 12 is about 16 pounds.

It will be apparent that many alternative and fully equivalent components and structures may be substituted for those here specifically described without departing from the spirit of the invention. For example, the motor unit may be directly connected to the printing roller, or the connection may be made through direct gearing or by other means. Likewise, means other than direct gearing may be employed for driving the drive rollers 11 and 12, although direct gear drives will ordinarily be preferred. In this connection, other means of producing differential surface speeds, contemplated as coming with in the invention, include direct driving of roller 12 at the same surface speed, and driving of roller 11 at a lesser surface speed, as compared with the surface speed of the printing roller 19. Controlled differential without roll slippage may also be attained by including a slipping clutch device in the drive mechanism for one or both of the drive rollers.

The simplified switching arrangement hereinbefore de scribed is adequate for most purposes. The switch 18, operating through suitable relays, simultaneously actuates both the motor 35 and the lamp 15; and operation of both motor and lamp continues until both of switches 18 and 19 have returned to the off position. Where desired, additional switches may be incorporated, or suitable delay means provided, to delay the activation of the lamp 15 until the leading portion of the carrier screen 60 has passed beneath both of the rollers 11 and 12, and then to permit the lamp to be de-actuated shortly after the trailing edge of the screen member has passed beneath roller 11.

Likewise the apparatus as described may be adjusted for different use conditions, for example by altering the speed of rotation of the printing roller through changes in the drive motor or sprockets, by varying the pressures on the drive rollers, by substituting drive rollers or carrier screens having different frictional surface characteristics, or by altering the lamp member or its positioning with respect to the printing roller, all as hereinbefore indicated. Once the desired adjustments have been made, however, there is provided a simple, readily portable, but fully eifective means for making copies of graphic originals by thermographic copying procedures and without subsequent manipulation of switches or control mechanisms.

What is claimed is as follows:

1. A thermocopying machine comprising a printing roller, a first drive roller and a second drive roller each axially parallel to said printing roller, a radiation source for directing a narrow intense beam of radiation along a generatrix of said printing roller between said first and second drive rollers, means for urging said drive rollers toward said printing roller, means for rotating said first drive roller and said printing roller at the same surface speed, and means for rotating said second drive roller at a surface speed somewhat greater than that of said printing roller.

2.. A thermocopying machine comprising a large-diameter rigidly smooth-surfaced printing roller having a central peripheral magnetic section, a small-diameter compressible first drive roller and a small-diameter compressible second drive roller each axially parallel to said printing roller, separated by approximately one quadrant along the circumference of said printing roller, and urged toward said printing roller; drive means for imparting uniform rotation to said printing roller; a first gear train for rotatively driving said first drive roller at the same surface speed as said printing roller; a second gear train for rotatively driving said second drive roller at somewhat greater surface speed than said printing roller; and irradiating means for intensely irradiating a web, carried by said printing roller, along a narrow line between and parallel to said first and second drive rollers.

3. A device suitable for continuously placing a composite of graphic original and heat-sensitive copy-sheet in heat-conductive pressure-contact while advancing said composite, comprising a large-diameter main roller having a smooth hard surface, a first small-diameter compressible roller and a second small-diameter compressible roller disposed parallel to said main roller and separated from each other by approximately one quadrant along the circumference of said main roller, means for urging each of said first roller and said second roller radially toward said main roller, means for rotating said main roller and said first roller at the same surface speed, and means for rotating said second roller at a surface speed somewhat greater than that of said main roller.

4. The device of claim 3 in which said main roller comprises a plurality of opposed axially magnetized narrow ring-like segments forming at least a central portion of the circumferential surface of said roller.

5. A carrier suitable for advancing a composite of printed paper and heat-sensitive copy-sheet through a thermocopying machine as described in claim 2 and comprising a flexible base having a ferromagnetic central forward edge section, and means just rearward of said section for temporarily retaining at least the forward edge of said composite against said base while permitting irradiation of said composite.

References Cited in the file of this patent UNITED STATES PATENTS Re. 25,079 Kollook Nov. 14, 1961 1,657,287 Trist Jan. 24, 1928 2,231,291 Morrison Feb. 11, 1941 2,375,603 Willard May 8, 1945 2,571,551 Eichenbaum Oct. 16, 1951 2,585,519 Van der Grinten Feb. 12, 1952 2,740,895 Miller Apr. 3, 1956 2,805,856 Stuchbery Sept. 10, 1957 2,916,622 Nieset Dec. 8, 1959 2,958,778 Miller et a1 Nov. 1, 1960 

1. A THERMOCOPYING MACHINE COMPRISING A PRINTING ROLLER, A FIRST DRIVE ROLLER AND A SECOND DRIVE ROLLER EACH AXIALLY PARALLEL TO SAID PRINTING ROLLER, A RADIATION SOURCE FOR DIRECTING A NARROW INTENSE BEAM OF RADIATION ALONG A GENERATRIX OF SAID PRINTING ROLLER BETWEEN SAID FIRST AND SECOND DRIVE ROLLERS, MEANS FOR URGING SAID DRIVE ROLLERS TOWARD SAID PRINTING ROLLER, MEANS FOR ROTATING SAID FIRST DRIVE ROLLER AND SAID PRINTING ROLLER AT THE SAME SURFACE SPEED, AND MEANS FOR ROTATING SAID SECOND DRIVE ROLLER AT A SURFACE SPEED SOMEWHAT GREATER THAN THAT OF SAID PRINTING ROLLER. 